The invention relates to a pipette with an ejection device for pipette tips.
Pipettes are used particularly in laboratories for dosing liquids. For this purpose, a pipette tip with an upper opening is clamped onto a shoulder of the pipette. The pipette tip can draw up and dispense liquid through a lower opening. Air displacement pipettes comprise a displacement device for air that is connected to the pipette tip communicating through the shoulder. An air buffer is transferred by the displacement device so that the liquid is aspirated into, and discharged out of, the pipette tip. The displacement device is typically a cylinder with a shiftable piston disposed therein.
After use, the pipette tips are detached from the shoulder, and exchanged for a fresh pipette tip. In this way, contamination of the subsequent dosings is avoided. Single-use pipette tips made of plastic are available and economical.
The shoulder for detachably retaining the pipette tips is a conical or cylindrical projection with respect to a housing of the pipette, and a pipette tip can be clamped thereupon with an upper opening adapted for this purpose. This can occur without handling the pipette tip, by pushing the pipette with the shoulder into the upper opening of the pipette tip that is ready in a retainer.
For avoiding contamination, known pipettes have an ejection device with a drive device. By actuating an ejector button, an ejection slide is shifted via an ejection rod such that it detaches the pipette tips from the shoulder without requiring the user to handle the pipette tip. These pipettes have a dosing button for actuating the displacement device and the separate ejector button for actuating the ejection device, such that two buttons must be actuated.
The document, DE 25 49 477 C3, the entire contents of which is incorporated herein by reference, discloses a manual pipette with one-button operation. This pipette has a housing from which an actuating element projects at the top that can be depressed counter to a spring effect, and that is connected via a stroke rod to a movable piston in a cylinder. When actuating the actuating element, the piston executes an adjustable working stroke. To blow out the remaining liquid from the pipette tip, the piston can perform an over-stroke. For this purpose, a separable magnet arrangement is present between the actuating element and the piston-cylinder unit that indicates the end of the working stroke to the user by a resistance, after overcoming of which, the over-stroke is performed. In addition, there is provided an ejection stroke for ejecting the pipette tip. For this purpose, the piston rod has a stop element that can slide an ejection sleeve at an actuating end so that the sleeve with an ejection end pushes the pipette tip at the upper edge thereof from the shoulder. The start of the ejection stroke is indicated to the user by the resistance of a spring acting on the ejection sleeve. During the ejection stroke, the piston is also moved such that free space is required in the cylinder. The free space forms a dead volume that influences the dosing accuracy.
The document DE 197 08 151 A1, the entire contents of which is incorporated herein by reference, describes a further pipette with one-button operation that has a smaller dead volume. The pipette has a movement device, a piston movable by this device in a cylinder for moving air, a fastening shoulder with a connection to the cylinder having an opening for fastening a pipette tip, and a stop for limiting the movement of the piston toward the opening of the fastening shoulder while moving air. The stop is a face surface of the cylinder upon which the piston strikes while pushing air toward the opening of the fastening shoulder. Further, the pipette has an ejection device which has an ejection section for separating a pipette tip from the fastening shoulder during an ejection movement of the ejection device, and an actuating section for effecting the ejection movement. In addition, there is a decoupling device that decouples the piston from the movement device upon reaching the stop. The decoupling device is formed by a magnet arrangement with a magnet and a magnetizable counterpart, which can be separated from each other after overcoming a retention force. A driver coupled to the movement device acts on the actuating section when the piston is decoupled, wherein a movement of the driver by the movement device forces the ejection movement of the ejection device. With this pipette, the movement of the piston after the working stroke, and possibly a blow out stroke for blowing out residual liquid, is limited by the stop. Then, the decoupling device decouples the piston from the movement device. With a further actuation of the movement device in the same direction, the piston is not moved further, however, a driver coupled to the movement device is moved which acts on the actuating section of the ejection device, and forces the ejection movement. The ejection movement without further movement of the piston reduces the dead volume, and improves the dosing accuracy.
In the disclosed pipette, the piston is stressed during contact on the face side of the cylinder, such that it must be designed to be sufficiently stable. With small sizes for small dosing volumes, this is costly. During the assembly, the upper housing part, which comprises the decoupling device and the piston, are screwed together with a lower housing part that comprises the cylinder. During the production of pipettes of different sizes for different dosing ranges, the upper parts of the housing must be populated with different decoupling devices and cylinders, and then combined with the respectively appropriate lower parts of the housing.
The document, DE 10 2004 003 434 B4, the entire contents of which is incorporated herein by reference, describes a pipette with a displacement device and a drive device detachably connected thereto. The displacement device has a displacement chamber with a shiftable boundary, a shoulder for connecting to a pipette tip, and a connecting channel between the displacement chamber and the free end of the shoulder. The drive device for driving the shiftable boundary of the displacement device has a drive element that has a detachble effective connection to the shiftable boundary. A bayonet connection between the drive device and the displacement device can be established by producing the effective connection between the drive element and the shiftable boundary, and can be detached by terminating the effective connection between the drive element and the shiftable boundary. The pipette has a separate ejection device for detaching a pipette tip from the shoulder, which ejection device has an ejection drive disposed separately at the drive device, an ejector disposed at the displacement device, and a detachable axial clamping connection between the ejection drive and ejector directed in the direction of the longitudinal axis of the bayonet connection.
Starting from this background, the object of the invention is to create a pipette that reduces the expense for providing different sizes and is easier to handle.
The objective is solved by a pipette with the features of claim 1. Advantageous embodiments of the pipette are specified in the dependent claims.